Solvation of a Small Metal-Binding Peptide in Room-Temperature Ionic Liquids

Shim, Youngseon,Kim, Hyung J.,Jung, YounJoon Korean Chemical Society 2012 Bulletin of the Korean Chemical Society Vol.33 No.11

Structural properties of a small hexapeptide molecule modeled after metal-binding siderochrome immersed in a room-temperature ionic liquid (RTIL) are studied via molecular dynamics simulations. We consider two different RTILs, each of which is made up of the same cationic species, 1-butyl-3-methylimidazolium ($BMI^+$), but different anions, hexafluorophosphate ($PF_6{^-}$) and chloride ($Cl^-$). We investigate how anionic properties such as hydrophobicity/hydrophilicity or hydrogen bonding capability affect the stabilization of the peptide in RTILs. To examine the effect of peptide-RTIL electrostatic interactions on solvation, we also consider a hypothetical solvent $BMI^0Cl^0$, a non-ionic counter-part of $BMI^+Cl^-$. For reference, we investigate solvation structures in common polar solvents, water and dimethylsulfoxide (DMSO). Comparison of $BMI^+Cl^-$ and $BMI^0Cl^0$ shows that electrostatic interactions of the peptide and RTIL play a significant role in the conformational fluctuation of the peptide. For example, strong electrostatic interactions between the two favor an extended conformation of the peptide by reducing its structural fluctuations. The hydrophobicity/hydrophilicity of RTIL anions also exerts a notable influence; specifically, structural fluctuations of the peptide become reduced in more hydrophilic $BMI^+Cl^-$, compared with those in more hydrophobic $BMI^+PF_6{^-}$. This is ascribed to the good hydrogen-bond accepting power of chloride anions, which enables them to bind strongly to hydroxyl groups of the peptide and to stabilize its structure. Transport properties of the peptide are examined briefly. Translations of the peptide significantly slow down in highly viscous RTILs.

Graphene-based supercapacitors in the parallel-plate electrode configuration: Ionic liquids <i>versus</i> organic electrolytes

Shim, Youngseon,Kim, Hyung J.,Jung, YounJoon The Royal Society of Chemistry 2012 Faraday discussions Vol.154 No.-

<p>Supercapacitors with two single-sheet graphene electrodes in the parallel plate geometry are studied <I>via</I> molecular dynamics (MD) computer simulations. Pure 1-ethyl-3-methylimidazolium tetrafluoroborate (EMI<SUP>+</SUP>BF<SUP>−</SUP><SUB>4</SUB>) and a 1.1 M solution of EMI<SUP>+</SUP>BF<SUP>−</SUP><SUB>4</SUB> in acetonitrile are considered as prototypes of room-temperature ionic liquids (RTILs) and organic electrolytes. Electrolyte structure, charge density and associated electric potential are investigated by varying the charges and separation of the two electrodes. Multiple charge layers formed in the electrolytes in the vicinity of the electrodes are found to screen the electrode surface charge almost completely. As a result, the supercapacitors show nearly an ideal electric double layer behavior, <I>i.e.</I>, the electric potential exhibits essentially a plateau behavior in the entire electrolyte region except for sharp changes in screening zones very close to the electrodes. Due to its small size and large charge separation, BF<SUP>−</SUP><SUB>4</SUB> is considerably more efficient in shielding electrode charges than EMI<SUP>+</SUP>. In the case of the acetonitrile solution, acetonitrile also plays an important role by aligning its dipoles near the electrodes; however, the overall screening mainly arises from ions. Because of the disparity of shielding efficiency between cations and anions, the capacitance of the positively-charged anode is significantly larger than that of the negatively-charged cathode. Therefore, the total cell capacitance in the parallel plate configuration is primarily governed by the cathode. Ion conductivity obtained <I>via</I> the Green-Kubo (GK) method is found to be largely independent of the electrode surface charge. Interestingly, EMI<SUP>+</SUP>BF<SUP>−</SUP><SUB>4</SUB> shows higher GK ion conductivity than the 1.1 M acetonitrile solution between two parallel plate electrodes.</p>

Graphene-Based Supercapacitors: A Computer Simulation Study

Shim, Youngseon,Jung, YounJoon,Kim, Hyung J. American Chemical Society 2011 The Journal of Physical Chemistry Part C Vol.115 No.47

<P>Energy density of supercapacitors based on a single-sheet graphene electrode is studied via molecular dynamics (MD) computer simulations. Two electrolytes of different types, pure 1-ethyl-3-methylimidazolium tetrafluoroborate (EMI<SUP>+</SUP>BF<SUB>4</SUB><SUP>–</SUP>) and an 1.1 M solution of EMI<SUP>+</SUP>BF<SUB>4</SUB><SUP>–</SUP> in acetonitrile, are considered as a prototypical room-temperature ionic liquid (RTIL) and organic electrolyte, respectively. Structure of ions near the electrode surface varies significantly with its charge density, especially in pure RTIL. Specific capacitance normalized to the electrode surface area is found to be higher in EMI<SUP>+</SUP>BF<SUB>4</SUB><SUP>–</SUP> than in acetonitrile solution by 55–60%. This is due to strong screening of the electrode charge by RTIL ions in the former. The RTIL screening behavior is found to be rather insensitive to temperature <I>T</I>. As a result, the capacitance of supercapacitors based on pure EMI<SUP>+</SUP>BF<SUB>4</SUB><SUP>–</SUP> decreases by less than 5% as <I>T</I> increases from 350 to 450 K. The difference in size and shape between cations and anions and the resulting difference in their local charge distribution as counterions near the electrified graphene surface yield cathode–anode asymmetry in the electrode potential in RTIL. As a consequence, specific capacitance of the positively charged electrode is higher than that of the negatively charged electrode by more than 10%. A similar degree of disparity in electrode capacitance is also found in acetonitrile solution because of its nonvanishing potential at zero charge. Despite high viscosity and low ion diffusivity of EMI<SUP>+</SUP>BF<SUB>4</SUB><SUP>–</SUP>, its overall conductivity is comparable to that of the acetonitrile solution thanks to its large number of charge carriers. The present study thus suggests that as a supercapacitor electrolyte, RTILs are comparable in power density to organic electrolytes, while the former yield considerably better energy density than the latter at a given cell voltage.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2011/jpccck.2011.115.issue-47/jp203458b/production/images/medium/jp-2011-03458b_0014.gif'></P>

Solvation of a Small Metal-Binding Peptide in Room-Temperature Ionic Liquids

Youngseon Shim,Hyung J. Kim,정연준 대한화학회 2012 Bulletin of the Korean Chemical Society Vol.33 No.11

Structural properties of a small hexapeptide molecule modeled after metal-binding siderochrome immersed in a room-temperature ionic liquid (RTIL) are studied via molecular dynamics simulations. We consider two different RTILs, each of which is made up of the same cationic species, 1-butyl-3-methylimidazolium (BMI+), but different anions, hexafluorophosphate (PF6 −) and chloride (Cl−). We investigate how anionic properties such as hydrophobicity/hydrophilicity or hydrogen bonding capability affect the stabilization of the peptide in RTILs. To examine the effect of peptide-RTIL electrostatic interactions on solvation, we also consider a hypothetical solvent BMI0Cl0, a non-ionic counter-part of BMI+Cl−. For reference, we investigate solvation structures in common polar solvents, water and dimethylsulfoxide (DMSO). Comparison of BMI+Cl− and BMI0Cl0 shows that electrostatic interactions of the peptide and RTIL play a significant role in the conformational fluctuation of the peptide. For example, strong electrostatic interactions between the two favor an extended conformation of the peptide by reducing its structural fluctuations. The hydrophobicity/hydrophilicity of RTIL anions also exerts a notable influence; specifically, structural fluctuations of the peptide become reduced in more hydrophilic BMI+ Cl−, compared with those in more hydrophobic BMI+ PF6 −. This is ascribed to the good hydrogen-bond accepting power of chloride anions, which enables them to bind strongly to hydroxyl groups of the peptide and to stabilize its structure. Transport properties of the peptide are examined briefly. Translations of the peptide significantly slow down in highly viscous RTILs.

Dielectric Relaxation and Solvation Dynamics in a Room-Temperature Ionic Liquid: Temperature Dependence

Shim, Youngseon,Kim, Hyung J. American Chemical Society 2013 The journal of physical chemistry. B, Condensed ma Vol.117 No.39

<P>Dielectric relaxation, related polarization and conductivity, and solvation dynamics of the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (BMI<SUP>+</SUP>PF<SUB>6</SUB><SUP>–</SUP>) are studied via molecular dynamics computer simulations in the temperature range 300 K ≤ <I>T</I> ≤ 500 K. Two main bands of its dielectric loss spectrum show differing temperature behaviors. As <I>T</I> increases, the absorption band in the microwave region shifts to higher frequencies rapidly, whereas the location of the bimodal far-IR band remains nearly unchanged. Their respective intensities tend to decrease and increase. The static dielectric constant of BMI<SUP>+</SUP>PF<SUB>6</SUB><SUP>–</SUP> is found to decrease weakly with <I>T</I>. The ultrafast inertial component of solvation dynamics remains largely unchanged, while their dissipative relaxation component becomes faster. Roles played by ion reorientations and translations in governing dynamic and static dielectric properties of the ionic liquid are examined. A brief comparison with available experimental results is also made.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpcbfk/2013/jpcbfk.2013.117.issue-39/jp406353j/production/images/medium/jp-2013-06353j_0009.gif'></P>

Nanoporous Carbon Supercapacitors in an Ionic Liquid: A Computer Simulation Study

Shim, Youngseon,Kim, Hyung J. American Chemical Society 2010 ACS NANO Vol.4 No.4

<P>Supercapacitors composed of carbon nanotube (CNT) micropores in the room-temperature ionic liquid (RTIL) 1-ethyl-3-methylimidazolium tetrafluoroborate (EMI<SUP>+</SUP>BF<sub arrange='stack'>4</SUB><sup arrange='stack'>−</SUP>) are studied <I>via</I> molecular dynamics (MD) computer simulations. It is found that the distribution of RTIL ions inside the micropore varies significantly with the pore size. Internal solvation of small (6,6) and (7,7) CNTs with an electrified interior wall is effected almost exclusively <I>via</I> counterions. Surprisingly, these counterions, even though they all have the same charge, lead to a charge density characterized by multiple layers with alternating signs. This intriguing feature is attributed to the extended nature of RTIL ion charge distributions, which result in charge separation through preferential orientation inside the electrified nanotubes. In the case of larger (10,10) and (15,15) CNTs, counterions and co-ions develop multilayer solvation structures. The specific capacitance normalized to the pore surface area is found to increase as the CNT diameter decreases from (15,15) to (7,7). As the pore size further reduces from (6,6) to (5,5), however, the specific capacitance diminishes rapidly. These findings are in excellent agreement with recent experiments with carbon-based materials. A theoretical model based on multiple charge layers is proposed to understand both the MD and experimental results.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2010/ancac3.2010.4.issue-4/nn901916m/production/images/medium/nn-2009-01916m_0009.gif'></P>

Correction to “Graphene-Based Supercapacitors: A Computer Simulation Study”

Shim, Youngseon,Jung, YounJoon,Kim, Hyung J. American Chemical Society 2012 JOURNAL OF PHYSICAL CHEMISTRY C - Vol.116 No.34

LSTM 및 회귀모델을 이용한 실내 공기질 예측 및 주거자 행동고지 알고리즘 연구

심영선(Youngseon Shim),최해진(Hae-Jin Choi) 대한기계학회 2022 대한기계학회 춘추학술대회 Vol.2022 No.5

LSTM 및 회귀모델을 이용한 실내 공기질 예측 및 주거자 행동고지 알고리즘 연구

심영선(Youngseon Shim),최해진(Hae-Jin Choi) 대한기계학회 2022 대한기계학회 춘추학술대회 Vol.2022 No.5

Effects of Alkyl Chain Length on Interfacial Structure and Differential Capacitance in Graphene Supercapacitors: A Molecular Dynamics Simulation Study

Jo, Sungsik,Park, Sang-Won,Shim, Youngseon,Jung, YounJoon Elsevier 2017 ELECTROCHIMICA ACTA Vol.247 No.-

<P><B>Abstract</B></P> <P>Supercapacitors with graphene electrodes are studied via molecular dynamics simulation. As an electrolyte, we consider three different room-temperature ionic liquids (RTILs), each of which is made up of the same anion BF<SUB>4</SUB> <SUP>−</SUP>, and different cations, 1-C<SUB>n</SUB>(n=2,4,6)-3-methylimidazolium, respectively. We investigate how the alkyl chain length of the cation affects their interfacial structure and electrical properties for electric double layer capacitors. As a whole, cations and anions make layering structures between two parallel electrodes. Cations in the nearest layer orient predominantly in parallel to the electrode. Imidazolium rings of cations form π-stacking with graphene, then the alkyl chains of cations align parallel to the electrode. Differential capacitances in three RTILs are found to decrease with an increase of the magnitude of electrode potentials. The ion size and orientation affect both structure and capacitance behavior. The parallel orientations of cations become stronger with an increase of the alkyl chain length for the considered RTILs. The differential capacitance tends to decrease with raising the alkyl chain length over a wide range of the electrode potential. This is ascribed to a steric effect caused by larger cation size. It is also found that anodic capacitance is higher than cathodic one due to a higher screening efficiency by small anions, and an asymmetry in the peak of capacitance biased to the cathodic side becomes weaker as the alkyl chain length increases. Comparing electrode charge with ion numbers near the electrodes, with respect to their changes in response to the electrode potential, we find that the interfacial layer of the electrolyte mainly governs capacitive behavior of the systems.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The structure and electrical properties of the supercapacitors consisting of imidazolium-based ionic liquids are studied via molecular dynamics simulation. </LI> <LI> A longer alkyl chain of cations results in an enhanced π-stacking with the graphene electrode, but a lower differential capacitance. </LI> <LI> Ionic layers are defined from the ion number density distribution as a function of electrode charge. </LI> <LI> differential ion capacity shows a good correlation with the differential capacitance, indicating the importance of the interfacial layer of the electrolyte. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>